Net Income Per Common Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Income Per Common Share
Weighted average shares used for the basic net income per share computation	232,403,586	220,979,955	228,932,782	214,039,692
Incremental shares from share-based compensation	165,577	63,664	128,980	49,937
Weighted average shares used for diluted net income per share computation	232,886,185	221,360,641	229,378,784	214,406,651
Unvested Shares
Net Income Per Common Share
Unvested shares from share-based compensation that were anti-dilutive	115,789	59,149	107,539	59,569
Convertible Partnership Units
Net Income Per Common Share
Weighted average partnership common units convertible to common shares that were dilutive	317,022	317,022	317,022	317,022
Unvested shares from share-based compensation that were anti-dilutive	419,546	529,161	429,988	531,839